enabled with --enable-python (defaults to auto-detect).
Thanks to some magic in python-yasm/Makefile.inc and setup.py, this actually
plays nicely with automake distcheck.
* m4/pythonhead.m4: Script to find Python.h.
* m4/Makefile.inc: Include it in distfiles.
* configure.ac: Add --enable-python option and Python and Pyrex detection.
* tools/Makefile.inc: Pull tools/python-yasm/Makefile.inc into build.
* python-yasm/Makefile.inc: Add automake build magic for extension.
* setup.py: Likewise.
svn path=/trunk/yasm/; revision=1456